1. Field of the Invention
This invention relates to a plate-like polarizing element, a polarizing conversion unit provided with the element, and a projector provided with the unit.
2. Related Background Art
As an apparatus for converting non-polarized light having a random plane of polarization into polarized light, an apparatus described in Japanese Laid-Open Patent Application No. 61-90584 is shown in FIG. 1 of the accompanying drawings.
In this projector, non-polarized parallel light emerging from a condenser lens 104 enters a polarizing beam splitter 111, and P-polarized light L.sub.P is intactly transmitted through the acting surface (evaporated film formed on an inclined surface on which two rectangular prisms are adhesively secured to each other) 111a of the polarizing beam splitter 111, while S-polarized light L.sub.S is upwardly reflected at a right angle and enters a total reflection prism 112. The S-polarized light L.sub.S is rightwardly reflected at a right angle by the total reflection prism 112, whereby it emerges from the total reflection prism 112 in the same direction as the P-polarized light L.sub.P transmitted through the polarizing beam splitter 111. The S-polarized light L.sub.S refers to rectilinearly polarized light having a plane of polarization parallel to the acting surface 111a of the polarizing beam splitter 111, and the P-polarized light L.sub.P refers to rectilinearly polarized light having a plane of polarization orthogonal to the S-polarized light L.sub.S. A half wavelength plate 113 is disposed on the emergence side of the total reflection prism 112, and the S-polarized light L.sub.S which has emerged from the total reflection prism 112 is transmitted through the half wavelength plate 113, whereby the plane of polarization thereof is rotated by 90.degree. and the S-polarized light L.sub.S is converted into P-polarized light L.sub.P *. Also, wedge type lenses 114 and 115 for changing optical path are disposed on the emergence sides of the polarizing beam splitter 111 and the half wavelength plate 113, respectively, and the P-polarized light L.sub.P transmitted through the polarizing beam splitter 111 and the P-polarized light L.sub.P * converted by the half wavelength plate 113 have their optical paths changed, and intersect each other at a point P.sub.0 on the incidence side surface of a liquid crystal light valve 117 and become combined light.
Accordingly, in this projector, the liquid crystal light valve 117 can be illuminated by both of the S-polarized light L.sub.S and the P-polarized light L.sub.P separated by the polarizing beam splitter 111. However, the above-described projector of Japanese Laid-Open Patent Application No. 61-90584 requires the large polarizing beam splitter 111 and total reflection prism 112, and this leads to the disadvantage that the entire apparatus becomes bulky and heavy.